Reasons to retrofit soft-story buildings
Ordinances are being enacted to prevent injury and loss of life, to reduce the displacement of residents, and to improve recovery times due to the potential for susceptible soft-story buildings to collapse during to significant ground motions during an earthquake. Research conducted by institutions of higher education, such as the full-scale buildings tested at the State University of New York at Buffalo and the University of California at San Diego [10], have supported the soft-story retrofit legislation.
History of damage to soft-story buildings due to past earthquakes
Most recently in the 6.9M Loma Prieta earthquake in 1989 (Northern California) and the 6.7M Northridge Earthquake in 1991 (Southern California), buildings with soft-story characteristics were subject to violent shaking resulting in significant damage and in some cases collapse, causing the loss of 16 people from just one such apartment collapse [5].
Basic definition of a soft-story building
The Structural Engineers Association of Northern California defines a soft-story building as those where: “Typically on the first floor level, a story that is weaker and/or more flexible than the stories above it for lateral force resistance. These first stories may be taller than the stories above, or may have large wall openings (such as garage doors) while the stories above have solid walls. Earthquakes can cause significant damage to structures with a soft story, as the soft stories often lean or collapse due to their lower stiffness and/or strength.” [6] The Los Angeles Times has published illustrations that depict how these types of buildings are vulnerable to earthquakes [8].
Settling on identifying characteristics
Various cities in California have settled on more detailed definitions, including year(s) of construction, number of units, number of stories, and other characteristics such as the presence of ground floor parking or other similar open floor spaces. These requirements are summarized in the applicable ordinances that have been enacted or are under consideration. A registered engineer with experience in soft-story retrofits should be familiar with the local code requirements in your jurisdiction.
Starting in 2009, the City of Oakland began to specifically screen buildings with the following characteristics [2]:
• Permitted for construction prior to adoption on January 1, 1991, of the 1988 edition of the Uniform Building Code
• With parking or commercial on the ground floor
• With 5 or more residential units (apartments, condos, or live-work)
• Not structurally retrofitted for earthquakes forces already
• 2+ stories
Steps to the enacted and proposed legislation across California
Typical residential buildings of conventional light-frame wood construction have proven to be one of the most earthquake-resistant structure types due to the inherent damping of the system when built in accordance with modern building codes. The structural engineering community is led by the efforts of practicing engineer members of the Structural Engineers Association of California (SEOAC). Through the latest academic and industry research and as a result of past earthquakes, professionals have recommended that the vulnerability of this specific type of building be addressed through legislation to require retrofit upgrades [7].
Learn more about soft-story retrofits in Oakland
To check whether your building is on the City of Oakland’s soft-story retrofit screening list, you can enter your property’s address using OpenOakland’s tool [2]. Additional details about the retrofit program, including reimbursement incentive programs and grants [4]. If your house or apartment complex is on the list, you may receive a notice from the city once the legislation is passed. At this point, it is recommended to hire a licensed Professional Engineer in the State of California to evaluate your existing building to determine whether a soft-story retrofit may be required.
Timeline to adoption
On December 11, 2018, the city council approved the first reading of the proposed soft-soft-story ordinance (#18-1062) [12]. This legislation would require owners of soft-story buildings containing 5 or more units to do the following:
• Within one year, a document that the building is exempt from the seismic retrofit program; or
• Within 4-6 years, depending on the type of building, perform a mandatory structural evaluation, obtain a retrofit permit(s), and complete retrofit work per specified engineering criteria. Some financial assistance is available for owners and zoning incentives apply, such as waived parking, setback and height regulations, and one or two additional dwelling units (ADUs) are permitted depending on the size of the building. Take advantage of this exception to the normal zoning requirements and combine your soft-story retrofit project with an addition project to improve the income-generating ability of your existing residential property today. Contact us to discuss the specifics of your property and learn about our bundled soft-story retrofit + ADU packages.
Other cities with soft-story retrofit ordinances
The city of Oakland has followed the example set by other jurisdictions in California, including those in the Los Angeles and San Francisco metropolitan areas, that have passed similar retrofit ordinances for soft-story buildings. Some of these cities include San Francisco, Berkeley, Alameda, Mountain View, Fremont, San Leandro, Los Angeles, Santa Monica, West Hollywood, and Beverly Hills. The Association of Bay Area Governments has released a model ordinance to help other cities currently in the process of enacting similar legislation [9].
The design process—first, an evaluation
The first step is to obtain the relevant information for the building’s structure and to perform a structural evaluation. Building plans can be obtained and other records can be obtained from the owner/property manager or from the city records department, if available. In the event that blueprints are not readily accessible, a structural site survey can be performed to observe the existing structure and document the existing conditions. In certain instances where plans are not available, select invasive testing may be required, in order to document the existing structural system of the building. This is followed by performing a structural analysis to evaluate the building’s ability to resist earthquake forces per Code. The best-case scenario is that the structural calculations performed to support that the building is adequate as-is to resist the Code-level seismic forces, and thus a retrofit may not be required. This is why it is critical to hire an engineer with subject matter expertise gained through the completion of similar projects. The engineers at Design Everest have completed over 3,000 residential projects and are up-to-date on all the latest cost-effective retrofit solutions available. Contact us now and we will provide you a FREE Consultation with a quote. We also provide virtual on-sites and virtual consultations.
If a retrofit is required, then use our expertise to develop plans and obtain a permit
Following a structural evaluation, if a retrofit is required, a licensed Engineer can be hired to design the upgrades for a retrofit, if required. Through the structural design process, two to three relevant options will be considered and the least expensive and invasive option will be selected to save on construction and temporary relocation costs (while the retrofit project is under construction). Further clarification via a Frequently Asked Questions section on soft-story retrofits is published by the Structural Engineers Association of Northern California [11].
Typical retrofit approaches
Typical retrofit strategies may involve a combination of the following solutions tailored to your property:
• Putting in anchor bolts and hold-down hardware at existing plywood shear wall locations
• Installing structural plywood to existing wall studs
• Adding additional sheathed wall lines at select locations
• Reinforcing existing susceptible walls with pre-manufactured plywood or steel shear walls (e.g. Simpson Strong-Tie, MiTek)
• Erecting steel cantilever columns
• Using pre-manufactured steel moment frames (e.g. Simpson Strong-Tie, MiTek, Paco) or fabricating custom steel moment frames
Each building is unique and through special attention to your project, our engineers can devise a custom strategy to retrofit your building and give you the peace of mind that you will be more prepared in the event of the next ‘Big One’. We have engineers ready to begin work on your soft-story retrofit project today. Contact us now and we will provide you a FREE Consultation with a quote. We also provide virtual on-sites and virtual consultations.
Most homeowners are not prepared for the next ‘Big One’
Nearly 9 out of 10 homeowners and less than 10% of commercial buildings [1] have an insurance policy that covers earthquake damage. Soft-story retrofit is an effective way to improve the performance of your building in the event of a significant seismic event. Make the investment today to save on future repair costs, avoid potential injuries and death, and possibly lower the cost of an earthquake insurance policy. For commercial buildings, in particular, a soft-story retrofit may allow a building owner to save on insurance costs once a Probable Maximum Loss report is prepared by a licensed Professional Engineer. If you have been considering a remodel (kitchen, open floor plan, skylights) or addition (accessory dwelling unit, second story addition, deck/patio, pool) to your house, you can bundle both a soft-story retrofit analysis and design along with the permitting documents for your improvement project in order to save costs on both engineering and construction. Take a look at some of the residential projects we have completed since 2005 here [3].
